Check the nomenclature of your file. Your file should contain a date using the following nomenclature: YYYYYMMDD_. To be taken into account by the import script, the date must be today's date.
Ex: If it is May 8, 2020 and you want your file to be imported into Symplify on May 9, 2020, then you must upload your file with the nomenclature 20200509_newsletter. If you upload a file with an earlier date, (ex: 20200507_newsletter), the file will not be imported.